Shuttle-type printers are a class of printers having a movable shuttle or carriage that traverses back and forth across a printing surface. A printhead is mounted on the shuttle and synchronized with shuttle movement to print desired images. The shuttle class of printers includes both impact printers, such as dot matrix and daisy-wheel printers, and non-impact printers, such as ink-jet printers.
A shuttle drive mechanism maneuvers the shuttle over the printing surface. The shuttle drive mechanism typically consists of a motor, and a belt and pulley assembly which operably couples the shuttle to the motor. Common motors used in such mechanisms include a DC motor which changes speed and direction in relation to the level and polarity of DC voltage applied thereto, and a stepper motor which changes speed and direction in response to intermittent pulses. The stepper motor is less effective at providing precise position control as compared to the DC motor plus shaft encoder; but, the stepper motor is advantageously less expensive than the DC motor and encoder.
One problem that plagues shuttle-type printers is the inherent lack of precise positional control due to mechanical tolerances of the shuttle drive mechanism. The motor and drive belt assembly possess manufacturing variances that induce slight, but acceptable, errors in the shuttle positioning process. These errors are manifest in assembled printers and vary from printer to printer. Accordingly, it would be advantageous to identify the inherent mechanical errors within an assembled printer and compensate for them.
Another problem associated with printers concerns maintaining consistent print quality. Generally, print quality tends to deteriorate over time. This deterioration may be the result of mechanical wear or other factors such change in ink drop-volume (for ink-jet printers) or variations in pin impact (for dot matrix printers). While degradation in print quality is traditionally detected by the user, it would be desirable to provide an automated approach to monitoring print quality.
Another problem relates to printer versatility. Printers are often called upon to print on a wide variety of recording media having different widths and printing surfaces. Common recording media include standard 81/2.times.11 inch paper, A4 paper, and B4 paper. Additionally, printers are increasingly used to print bar codes or other information on narrow, adhesive-backed labels. Prior art printers detect various paper size using complex media feed sensors provided in the printer throat, or by sensing the type of tray used to store the media that is inserted into the printer. It would be advantageous to provide a simple, low cost method for detecting media width.
Aspects of this invention overcome the above drawbacks by providing a low cost, automated system and associated operating methods for determining absolute carriage position relative to the platen, monitoring print quality, and measuring media width.